Microwave antenna



Aug. 26, 1952 N. 1. KORMAN MICROWAVE ANTENNA Filed Feb. 17, 1950 INVENTOR Imrmam f 105mm 7 ATTORNEY I2 is excited in the TEo,1 mode. As well understood in the art, if there are a sufiicient number of circumferentially equally spaced slots M, the slots having an axial length greater than their width, the radiation pattern of the waveguide radiator portion I2 is substantially omnidirectional in character. In practice, four slots equally spaced circumferentially are usually suificient. The slotted waveguide i2 is merely an exemplification of any one of various radiators having such omnidirectional radiation characteristics.

A set of substantially parallel metallic plates I6 surround the waveguide radiator portion 12 substantially in planes normal to the predetermined axis 8 about which the omnidirectional radiation is directed. The plates I6 have varying inner and outer diameters, and those near the top and bottom of the structure, as apparent from Fig. 2, have a greater radial depth than those near the center of the structure. The horizontally polarized energy passing between these plates 16 travels at a phase velocity greater than the velocity of light whereby the plates 16 act as a lens element giving the energy high directivity in planes normal to the axis 8. The lens element illustrated here is by way of exemplification. There are other lens elements of parallel metallic plates suitable for the purpose, for example, those respectively shown in Figs. 1-5 of my co-pending application, Serial No. 1634, filed January 10, 1948, entitled An Antenna for .Microwave Beacons.

The lens element plates l6 are substantially entirely surrounded by a second set of substantially parallel metallic plates [8 which, however, lie in planes inclined substantially at 45 angles to the axis 8, It will be understood that it may not be possible to arrange the plates 18 to be parallel in a mathematically perfect sense although they will be parallel substantially and in a descriptive sense as viewed by an observer from a point a considerable distance from the antenna in a central plane normal to the axis 8.

Thus energy directed from the outer edge of the plates I6 with the electric vector horizontal strikes the inner edge of the space between the plates l8. The plates [8 are inclined at an angle of 45 to the axis 8 and the electric vector of the incident energy. Considering the energy now as being resolved into two portions, that polarized normal to the plates l8 and that polarized parallel to the plates IE, it i apparent that a phase shiftbetween the two is readily secured depending upon the radial depth of the plates l8 and the separation between them. This phase shift between the resolved energy portions may be made substantially 90, whereupon the energy emitted from the spaces between the plates [8 is directed outwardly as circularly polarized energy. The sense of rotation of the circular polarization depends upon the sense of inclination of the plates l8, being in one sense of rotation with the lates (8 inclined in one sense with respect to the axis .8 and being in a countersense of rotation with the plates I8 inclined in the other sense with respect to the axis 8. The energy from the antenn a a whole is circularly polarized, is substantially omnidirectional about the axis 8, and has high directivity in radial planes through the axis 8.

Referring now to Figs. 3 and 4, respectively cross sectional and plan views of another embodiment of the invention, a coaxial line section 20 has a circumferential slot 22 whereby the section 20 radiates vertically polarized energy.

The ection 20 is fed by a transmission line 2|. A set of plates 24 are arranged in radial planes about the axis 8 and symmetrically surround the radiator coaxial line section 20. The radial depth of the plates 24, considering their number, is made sufficiently short with respect to the distance of the plates from the axis 8 that the plates may be considered to be substantially parallel even though they are actually in radial planes. It is obviously also possible to thicken the outer edges of the plates 24 to be wedge-shaped whereby adjacent surfaces of adjacent plates are parallel, but I prefer for reasons of simplicity to use planar plates, as shown in Fig. 4. Surrounding the plates 24 are arranged a set of substantially parallel metallic plates l3 which may be the same as the plates [8 of Fig. 1.

In the operation of the arrangement of Fig. 4 the axis 8 may be assumed vertical. The vertically polarized energy from radiating line section 20 travels for a longer time at the same phase velocity between the upper and lower ends of plates 24 than it does between the central portions thereof, whereby the energy radiated therethrough is given a high directivity in planes through the axis 8 by suitable design of the contours of the plates 24,. The planes of the plates it are inclined at an angle of 45 to the vertical whereby as before a suitable phase shift of a portion of the energy results in circular polarization as it is emitted from the antenna. Energy radiated from the antenna of Fig. 4 is circularly polarized and has high directivity in any plane through the axis 8.

Referring now more particularly to Fig. 5 which is a cross sectional view of still another embodiment of the invention, a transmission line 19 feeds a radiator 26 having circularly polarized characteristics and having a radiation pattern substantially omnidirectional with respect to a predetermined axis I9. The radiator 25 may comprise a section of coaxial transmission line having circular aperture 2'! located centrally of the antenna. A set of metallic plates 28 surrounds the axis l9 and radiator 26. The plates 28 are arranged substantially symmetrically with respect to the axis' 19. These plates may be the same as the plates 24 of Figs. 3 and 4 except that the radially inner and outer contoursv may be diiferent. A second set of substantially parallel metallic plates 30 surrounds the first set and these plates 30 may be, the same as the plates l6 of Figs. 1 and 2, except that they may have different inner and outer contours. In operation, the circularly polarized energy from radiator 26 has one component thereoi focused by the plates 25 and the other component normal thereto focused by the plates 28, whereby .the circular polarization may be maintained, provided that the energy emitted at any point on radiator 26 as it travels radially outward has both the vertical and horizontal component shifted in phase by substantially the same amount in its travel between the plates 25 and 28 respectively. Simple calculation by those skilled in the art yields the necessary design relationship. The inner plates of Fig. 5 may be interchanged in position with the outer, as illustrated for example in Fig. 6, wherein the plates 30 and 28 have had their positions interchanged from thoseshown in Fig. 5.

In view of the foregoing description it will be apparent that there is disclosed a novel and highly useful antennahaving circular polarization characteristicsv together with all the advantages thereof and having an omnidirectional radiation pattern with respect to a predetermined axis and having high directivity in radial planes through said axis.

What I claim is:

1. An antenna comprising a central radiator or receptor having a radiation pattern substantially non-directional about a predetermined axis, a first set of substantially parallel metallic plates surrounding said radiator or receptor, and

' a second set of substantially parallel metallic plates surrounding said first set, both the said sets of plates being arranged substantially symmetrically about said axis whereby the antenna radiation pattern is substantially omnidirectional about said axis, at least one of said sets of plates being arranged as a metallic lens element to cause the radiation pattern from said antenna to have high directivity in any plane through said axis.

2. The antenna claimed in claim 1, said first set of plates lying in planes normal to said axis.

3. The antenna claimed in claim 1, said first set of plates lying in planes normal to said axis and being arranged as said lens element, said second set of plates lying substantially in planes inclined each substantially at an angle of 45 with said axis, whereby circular polarization of radiated energy is realized.

4. The antenna claimed in claim 1, said first set of plates lying substantially in radial planes through said axis and. being arranged as said lens element.

5. The antenna claimed in claim 1, said first set of plates lying in radial planes through said axis and being arranged as said lens element, said second set of plates lying substantially in planes inclined each substantially at an angle of 45 with said axis, whereby circular polariza tion of radiated energy is realized.

6. The antenna claimed in claim 1, said secon set of plates lying substantially in radial planes through said axis, and being arranged as a second set of plates lying substantially in planes inclined each substantially at an angle of with said axis and being all of the same radial depth.

8. The antenna claimed in claim 1, said second set of plates lying in planes normal to said axis.

9. The antenna claimed in claim 1, said second set of plates lying in planes normal to said axis and having different radial depths to serve as said metallic lens element.

10. The antenna claimed in claim 1, said first set of plates being arranged as said lens element, said second set of plates lying in planes normal to said axis and having differing radial depths thereby to be arranged as a second lens element to enhance energy focus in planes through said axis, said radiator or receptor having circular polarization characteristics.

11. An antenna comprising a central radiator or receptor having a radiation pattern substantially non-directional about a predetermined axis, a first set of substantially parallel metallic plates surrounding said radiator or receptor, and a second set of substantially parallel metallic plates surrounding said radiator or receptor, the plates of one of said sets being disposed normally to those of the other, each of said sets of plates being arranged symmetrically about said axis, whereby the radiation pattern is substantially omnidirectional about said axis, at least one of said sets of plates being arranged as a metallic lens element to cause the radiation pattern from said antenna to have high directivity in any plane through said axis.

NATHANIEL I. KORMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES: PATENTS 

